LCD columnar spacers made of a hydrophilic resin and LCD orientation film having a certain surface tension or alignment capability

ABSTRACT

A liquid crystal display using a hydrophobic material as the material of resinous columns to orient the molecules of the liquid crystal parallel to the substrates. A hydrophilic material can also be used as the material of resinous columns to orient the molecules of the liquid crystal vertical to the substrates. The liquid crystal molecules are oriented horizontally by making the surface tension of the orientation film greater than the surface tension of the resinous columns. The liquid crystal molecules are oriented vertically by making the surface tension of the orientation film smaller than the surface tension of the resinous columns. A mixture of a liquid crystal material and an uncured resin is placed in a liquid crystal cell. The uncured resin is precipitated (deposited) out of the mixture. The molecules of the liquid crystal material are oriented. Then, the uncured resin is cured. Thereafter, an aging step for reorienting the molecules of the liquid crystal material is carried out. This prevents disturbance of the orientation around the resinous columns and leads to an improvement in the voltage holding ratio.

This is a Divisional application of Ser. No. 08/245,045, filed May 17,1994, now U.S. Pat. No. 5,539,545.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal electro-optical devicehaving resinous columns which are formed by precipitating (depositing)an uncured resin out of a mixture of a liquid crystal material and theuncured resin and curing the precipitated (deposited) resin. The presentinvention also relates to a method of fabricating a liquid crystalelectro-optical device by holding a nematic liquid crystal orferroelectric liquid crystal between substrates, orienting the moleculesof the liquid crystal in a given direction, and switching the liquidcrystal molecules between different states electro-optically, usingpolarizing plates, the electro-optical device having resinous columnsprecipitated (deposited) out of the liquid crystal material.

BACKGROUND OF THE INVENTION

It is common practice to disperse spacers such as spherical silica beadsseveral micrometers in diameter between substrates in order to maintainthe spacing between the substrates inside the liquid crystal cell in aliquid crystal electro-optical device. Where spacers are used, adecrease in the substrate spacing can be prevented but an increase inthe spacing cannot be prevented. As the area of display screen isincreased, the substrates are distorted or the distribution of theliquid crystal material becomes more nonuniform. These spacers can by nomeans prevent these undesirable situations.

A countermeasure taken against this is to use a method consisting ofadding adhesive particles to the spacers and dispersing these particlesin the cell so as to maintain the substrate spacing. In this method,however, the orientation around the adhesive tends to be disturbed.

A method of solving the problem with the method of maintaining thesubstrate spacing has been proposed by the present inventors and othersas disclosed in Japanese Patent application Ser. No. 55237/1993. Inparticular, the substrate spacing is maintained by polymerized columnspacers which consist of resinous columns precipitated (deposited) outof a liquid crystal material. More specifically, a mixture of the liquidcrystal material and an uncured resin is inserted between substrates.The molecules of the liquid crystal material are oriented. The resinousmaterial is precipitated (deposited) and cured to form resinous columns.Both substrates are bonded together with these columns.

In this method, the resinous columns can be cured while the liquidcrystal molecules are oriented inside the cell. The liquid crystal isprecipitated (deposited) out of the mixture of the liquid crystalmaterial and the uncured resin, and the molecules of the liquid crystalare oriented. As a result, the resin is shaped. In consequence, thesubstrate spacing can be maintained while greatly suppressingdisturbance of the orientation around the resin.

A known liquid crystal electro-optical device using a PCS is shown inFIG. 1. This device comprises transparent substrates 110, 111,electrodes 112, 113, orientation films 114, 115, a liquid crystalmaterial 116, spacers 118, and a sealing material 119. Resinous columns117 are formed by precipitating (depositing) a resin out of a mixture ofthe liquid crystal material and an uncured resin and then curing theresin. These resinous columns are bonded to both orientation films 114and 115 to thereby maintain the substrate spacing. Where an orientationfilm is formed on only one electrode, one side of each resinous columnis bonded to the corresponding electrode or substrate.

Resins shrink greatly in volume on curing. This is a disadvantage with aPCS. Specifically, after a resin and a liquid crystal separate, themolecules of the liquid crystal are oriented without difficulty arounduncured resin. As the resin is cured, it shrinks, thus disturbing theorientation. This deteriorates the optical characteristics, especiallythe characteristic in dark state. Hence, the contrast drops.

These optical characteristics may not stable, i.e., may vary with alapse of time. One factor representing the stability of thesecharacteristics is a voltage holding ratio. In particular, a voltage isapplied to a pixel in a short time and then the application is stopped.The voltage holding ratio is the ratio of the remaining voltage to theapplied voltage. In other words, this factor expresses the degree towhich the liquid crystal molecule orientation is maintained. Therefore,in order to increase the voltage holding ratio, the liquid crystalmolecules should be more stable, and the orientation should be moreuniform.

In a liquid crystal electro-optical device using a PCS, when the liquidcrystal molecules are urged to be oriented uniformly along the rubbingdirection of the orientation film, the molecules might be orientedvertically or randomly, even if the same liquid crystal and the sameresin are used.

One factor affecting the orientation of liquid crystal molecules is aforce of the orientation film that restricts the liquid crystalmolecules. This restricting force of the orientation film attracts theliquid crystal molecules. Simply, this force is given by surfacetension, which is affected by various factors such as the kind oforientation film, baking temperature, film thickness, and the structureof the orientation film surface including rubbing.

Also, the surface tension of the PCS (polymerized column spacer) is amajor factor which affects the orientation of liquid crystal molecules.The surface tension varies, depending on whether the resin is anoligomer, a monomer, or a combination thereof.

The orientation of the liquid crystal material of a liquid crystalelectro-optical device using a PCS is exactly the same as theorientation of a normal liquid crystal display having no resin exceptaround the PCS. However, the liquid crystal molecules around the PCS arerestricted not only by the orientation film but also by the PCS. Thisdeteriorates the orientation.

In recent years, large area liquid crystal displays have attractedattention. Where cheap glass substrates or resinous substrates (plasticsubstrates) are used for large area displays, the substrates themselvesare distorted. Furthermore, designing a liquid crystal display operatingat a high speed is a matter of great concern and has been studied. Tosatisfy these requirements, use of a fast-response liquid crystalmaterial such as a ferroelectric liquid crystal may be contemplated.

However, where a ferroelectric liquid crystal is used as the liquidcrystal material to accomplish a fast response, it is impossible tofabricate a large area liquid crystal display, for the following reason.A ferroelectric liquid crystal has a layered structure and so if thesubstrates are deformed, this layered structure is destroyed. Thishinders displaying an image. This problem is not restricted toferroelectric liquid crystals but essentially takes place where variousliquid crystal materials are used.

In the past, silicon oxide spacers held between substrates have beenused to hold the substrate spacing, and an organic resinous materialheld between the substrates has been used to maintain the substrates inintimate contact with each other. Literally, spacers are employed tohold the substrate spacing. The substrate spacing is determined by thediameters of the spacers. The organic resin used to maintain substratesin intimate contact with each other has a larger diameter than therequired substrate spacing. Organic resin spacers are crushed betweenthe substrates and thus the two substrates are brought into intimatecontact with each other.

The prior art configuration described above has been essentiallyfabricated in the manner described now. The substrate surfaces are firstoriented. Then, the above-described spacers and resin are dispersed onone substrate. Subsequently, the substrates are bonded together. In thisway, the substrate spacing is determined. Thereafter, a liquid crystalmaterial is injected between the substrates. During this injection, themolecules of the liquid crystal material can be oriented according tothe orientation-restricting force of the orientation film, by heatingthe liquid crystal material, for example at 100° C., and then slowlycooling the material at a rate of 5° C./hr.

We have discussed the above-described manufacturing process and foundthat the resinous material for maintaining the substrates in intimatecontact with each other restricts movement of the liquid crystalmolecules when they are being oriented and are changing their state.

In an attempt to solve the above-described two problems, i.e., (1) astructure for maintaining the substrate spacing is needed and (2) whenthe molecules of the liquid crystal material are oriented, the materialfor maintaining the substrates in intimate contact with each otheradversely affects the orientation of the liquid crystal material, wehave devised a method as disclosed in the above-cited Japanese Patentapplication Ser. No. 55237/1993. In this method, a pair of transparentsubstrates having electrodes on their surfaces are disposed opposite toeach other such that the electrodes are located inside. A liquid crystalmaterial is placed between the substrates. Orientation means is providedon the inner surface of at least one substrate to orient the moleculesof the liquid crystal material in a given direction. Uncured resincontained in the liquid crystal material is precipitated (deposited) andcured to form resinous columns. These columns are in intimate contactwith the orientation means or with the substrate.

In order to fabricate this liquid crystal electro-optical device, amixture of the liquid crystal material and a resinous material to whicha reaction initiator has been added is sealed in between the transparentopposite substrates whose surfaces have been oriented. The molecules ofthe liquid crystal material are oriented and then the resinous-componentis cured by UV irradiation and shaped into columns.

The structure described above is briefly described now by referring toFIG. 1. Shown in this figure is a simple matrix liquid crystal displayhaving transparent substrates 110 and 111 equipped with electrodes 113and 112, respectively. Orienting means 114 and 115 for orienting theliquid crystal material molecules in given directions are formed on thesubstrates, respectively. The liquid crystal material, indicated by 116,is sandwiched between the substrates. The molecules of the liquidcrystal material 116 are oriented along their respective one axes by theorienting means 114 and 115. A resin 117 is separated and precipitated(deposited) from the liquid crystal material, and is shaped intocolumns. These resinous columns are bonded to the orienting means 114and 115 on the substrates 110 and 111, respectively. Where orientationmeans is provided on only one substrate, the resinous columns 117 arebonded either to the orienting means 114 and the transparent substrate111 or to the substrate 111 and the electrodes 113.

This liquid crystal electro-optical device is fabricated in the mannerdescribed now. A mixture of the liquid crystal material and the uncuredresin to which the reaction initiator has been added is held between thetransparent substrates 110 and 111 having the electrodes 113 and 112,respectively. The uncured resin is precipitated (deposited) out of themixture between the substrates to orient the liquid crystal moleculesalong the orientation means. Then, the precipitated (deposited) resin iscured into the columns 117. These bond together the substrates.

Where the structure shown in FIG. 1 is adopted, the molecules of theliquid crystal material 116 are oriented by the orienting means 115 andthen the resin is cured. Therefore, good orientation of the liquidcrystal prior to the curing can be maintained. The cured resin littleaffects the orientation. The resinous columns 117 maintain the substratespacing. In addition, the columns improve the adhesion of thesubstrates. Furthermore, the columns enhance the orientation of theliquid crystal molecules.

Preferably, the resinous material used in the above-described structureshows a mixture state with the liquid crystal material at hightemperatures and is separated and precipitated (deposited) from theliquid crystal material in low temperatures.

It is very desired that the uncured resin contain no solvent in order tocure the resin when it is held between the substrates. Since theseparation into the liquid crystal material and the resin and theorientation of the liquid crystal material depend heavily ontemperature, it is desired to cure the resin independent of temperature.Considering these factors into consideration, we can say that using a UVcurable resin as the uncured resin and ultraviolet radiation as theresin-curing means is desired. In the above-described configuration,limitations are imposed neither on the kind of the liquid crystalmaterial nor on the operating mode of the liquid crystal.

Where liquid crystal molecules are oriented parallel to thesubstrates-in operation, it is necessary that these liquid crystalmolecules obey the orientation-restricting force. However, where theresinous component is precipitated (deposited) into columns in theliquid crystal, the liquid crystal molecules are observed to be orientedparallel to, and along, the resinous columns around these columns. Thismeans that the long axes of some liquid crystal molecules are orientedvertical to the substrates, although the long axes of all liquid crystalmolecules must be oriented parallel to the substrates. If thedisturbance of the orientation becomes conspicuous, the opticalcharacteristics, especially the dark state characteristic, deteriorate.This leads to a decrease in the contrast. That is, where the resinouscomponent is precipitated (deposited) into columns out of the liquidcrystal mixture, the contrast is deteriorated in practice.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of fabricating a liquid crystal electro-optical device byprecipitating (depositing) resinous columns out of the aforementionedliquid mixture (i.e., a liquid crystal material and an uncured resin towhich a reaction initiator has been added), maintaining the substratespacing by these resinous columns, and maintaining the substrates inintimate contact with each other by the columns. This method ischaracterized in that the orientation is controlled to improve thecontrast. An electro-optical device according to the present inventioncomprises:

a pair of substrates;

an electro-optical modulating layer provided between the substrates andcomprising a liquid crystal material and a resinous material; and

a columnar spacer provided between the substrates and comprising theresinous material. The resinous material is adhesive.

It is another object of the invention to provide a liquid crystalelectro-optical device which uses a PCS (polymerized column spacer) andin which restricting force acting on liquid crystal molecules iscontrolled to improve the orientation.

It is a further object of the invention to provide a liquid crystalelectro-optical device which uses resinous columns precipitated(deposited) out of a liquid crystal material and in which disturbance ofthe orientation of the liquid crystal molecules around the columns isprevented even if the volume decreases after curing, thus improving theorientation, the voltage holding ratio, and the optical characteristics.

We conducted fundamental experiments on the structure for precipitating(depositing) resinous columns out of a mixture of the above-describedliquid crystal mixture and an uncured resin to which a reactioninitiator has been added and have found the following facts.

Where the long axes of liquid crystal molecules are orientedsubstantially parallel to the substrates, as the hydrophobic property ofthe resinous columns which stand vertical to the substrates isincreased, the restricting force of the resin acting on the liquidcrystal molecules weakens. As the force of the resinous columnsattracting the liquid crystal is reduced, the restricting force weakens.That is, the restricting force of the resinous columns acting on theliquid crystal can be reduced by enhancing the hydrophobic property ofthe resinous columns.

Accordingly, it is a yet other object of the invention to provide aliquid crystal display which shows improved contrast and in whichresinous columns do not exert an orientation-restricting force on liquidcrystal molecules.

A first embodiment of the invention is a liquid crystal displaycomprising a pair of substrates and a mixture of a liquid crystalmaterial and a resinous material, the mixture being held between thesubstrates. The molecules of the liquid crystal material is orientedparallel to the substrates. The resinous material contains a hydrophobicmaterial. The substrates are maintained in intimate contact with eachother by columns made from the resinous material.

In this embodiment, the resinous columns or cylinders for maintainingthe substrates in intimate contact with each other is hydrophobic innature. This eliminates the effect of the orientation-restricting forceof the resinous columns acting on the liquid crystal molecules. As aresult, only the orientation-restricting force of the orienting meansformed on the substrates orients the liquid crystal molecules.

Especially, where the liquid crystal molecules are oriented parallel tothe substrates, the elimination of the orientation-restricting forceacting vertical to the substrates is quite effective in enhancing theorientation of the liquid crystal.

The optimum liquid crystals used in the present embodiment areferroelectric liquid crystals because they have a layered structure andare easily affected by bending of the substrates. However, the presentinvention is not limited to ferroelectric liquid crystals. Rather, theinvention can be applied to all liquid crystal displays which areaffected by bending of the substrates.

A second embodiment of the present invention is a liquid crystal displaycomprising a pair of substrates and a mixture of a liquid crystalmaterial and a resinous material. The liquid crystal material isoriented vertical to the substrates. The resinous material contains ahydrophilic material. The substrates are held in intimate contact witheach other by columns made from the resinous material.

This embodiment has been made in view of the fact that where liquidcrystal molecules are urged to be oriented substantially vertical(orthogonal) to the substrates, if an orientation-restricting force actson the liquid crystal molecules parallel to the resinous columns whichhold the substrates in intimate contact with each other, then desirableresults are obtained. In particular, the resinous columns are made froma hydrophilic material, and the orientation-restricting force acting onthe liquid crystal molecules is parallel to the resinous columns. Thispromotes vertical orientation of the liquid crystal molecules withrespect to the substrates.

The liquid crystal display according to the second embodiment may have ahomeotropic alignment film provided o at least one of the substrates andin contact with the liquid crystal material. For example, thehomeotropic alignment film is a film using a silane coupling agent or asilicon oxide obliquely deposited film.

In the embodiments described above, it is advantageous to fabricate theresinous columns from a material which exhibits hydrophobic orhydrophilic property.

Where the resinous columns are made from a resinous material whichenhances the hydrophobic nature, the orientation-restricting force ofthe resinous columns acting on the liquid crystal molecules can beweakened. Most of the force acting on the liquid crystal molecules isthe restricting force produced by the orienting means. As a result, theliquid crystal molecules are oriented well.

Where a hydrophilic material is added to the resinous columns, verticalorientation of the liquid crystal molecules with respect to thesubstrates is promoted because the resinous columns positively exert anorientation-restricting force on the molecules.

A third embodiment of the invention is a method comprising the steps of:preparing a mixture of a liquid crystal material and an uncured resin;placing the mixture between a pair of transparent substrates disposedopposite to each other; precipitating (depositing) the uncured resin outof the mixture; orienting molecules of the liquid crystal material;curing the uncured resin; and reorienting the molecules of the liquidcrystal material. First, the uncured resinous material is precipitated(deposited) out of the mixture of the liquid crystal material and theuncured resin by slow cooling or other method, the mixture being held inthe cell. The molecules of the liquid crystal material are oriented.Then, the uncured resin is cured. At this time, the resin shrinks,causing a disturbance of the orientation of the liquid crystal moleculesaround the resin. Subsequently, the molecules are reoriented, forexample by heating and slow cooling. This step will hereinafter bereferred to as the aging step. In consequence, disturbance of theorientation around the resin is removed. Hence, the voltage holdingratio is improved. This leads to an improvement in the opticalcharacteristics.

A fourth embodiment of the invention is a liquid crystal electro-opticaldevice comprising a pair of substrates, an electro-optical modulatinglayer provided between the substrates and comprising a liquid crystalmaterial and a resin, an orientation film formed on the inner surface ofat least one of the substrates to orient molecules of the liquid crystalmaterial in a direction substantially parallel to the substrates, and acolumnar spacer provided between the substrates and comprising theresin. This embodiment is characterized in that the surface tension ofthe orientation film is greater than that of the columnar spacer.

A fifth embodiment of the invention is a liquid crystal electro-opticaldevice comprising a pair of substrates, an electro-optical modulatinglayer provided between the substrates and comprising a liquid crystalmaterial and a resin, an orientation film formed on the inner surface ofat least one of the substrates to orient molecules of the liquid crystalmaterial in a direction substantially orthogonal to the substrates, anda columnar spacer formed between the substrates and comprising theresin. This embodiment is characterized in that the surface tension ofthe orientation film is smaller than that of the columnar spacer.

In a liquid crystal electro-optical device using a polymerized columnspacer (PCS) according to the invention, the attracting force of theorientation film (simply, its surface tension) acting on liquid crystalmolecules of the resin is controlled at will to control the orientationof the molecules of the liquid crystal material. In this way, theorientation is improved.

Generally, as the surface tension increases, the force attracting liquidcrystal molecules increases. Therefore, where the liquid crystalmolecules are oriented parallel to the orientation film (i.e., thepretilt angle made with respect to the substrate surfaces is about0°-45°), the orientation is improved by increasing the surface tensionof the orientation film and reducing the surface tension of the PCS.Where the liquid crystal molecules are oriented vertical to theorientation film (i.e., the pretilt angle made with respect to thesubstrate surfaces is about 45°-90°), the orientation is improved byreducing the surface tension of the orientation film and increasing thesurface tension of the PCS.

Various methods can be utilized to control the surface tensions. Forexample, the composition of the material is varied. The baking time, thebaking temperature, the dilution concentration, the film thickness, orother factor of the material is changed. The surface shape is varied. Acoupling agent is applied. An appropriate method may be selectedaccording to the circumstances. In this way, in a liquid crystalelectro-optical device using a polymerized column spacer according tothe invention, the restricting force acting on the molecules of theliquid crystal material is controlled, thus improving the orientation.

Other objects and features of the invention will appear in the course ofthe description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a liquid crystal electro-optical deviceaccording to the invention;

FIG. 2 is a graph illustrating the relation of the photomultipliersensitivity to the contact angle of the pure water with respect to theadded resin of Example 1 of the invention in bright state;

FIG. 3 is a graph similar to FIG. 2 but illustrating the relation indark state; and

FIG. 4 is a graph illustrating the relation of the contrast ratio to thecontact angle of Example 1.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1

A liquid crystal electro-optical device according to the present exampleis schematically shown in FIG. 1. This device comprises substrates 110and 111 each of which is made of a glass substrate measuring 10×10 cm.ITO was sputtered on the glass substrates 110 and 111 to a thickness of1000 Å. The resulting films were photolithographically patterned to formelectrodes 112 and 113. Polyimide was applied to a thickness of 150 Å byspin coating. The laminate was baked at 280° C. and then rubbed to formorientation films 114 and 115 which are orienting means. RN-305 producedby Nissan Kagaku Kogyo, Japan, and LP-64 produced by Toray, Japan, wereused as the polyimide.

Thereafter, the orientation films 114 and 115 made of polyimide wereoriented in a known manner to orient the molecules of the films alongone axis. Spherical silica particles manufactured by Shokubai Kasei,Japan, were dispersed as spacers on one of the substrates 110 and 111.The sealing material 119 of epoxy resin was screen printed on the othersubstrate. The substrates were bonded together such that the spacingbetween their electrodes was about 1.5 μm. A mixture 116 of a liquidcrystal material and an uncured resinous material was injected into thecell between the substrates, thus completing a liquid crystal cell.

The liquid crystal material used in the present example wasferroelectric liquid crystal CS1014 produced by Chisso Corporation,Japan. Ps of this liquid crystal material was 5.4 nC/cm². The phasesequence was I (isotropic phase)-N (nematic phase)-A (smectic A phase)-C(smectic C* phase).

The resinous material used in the present example is a mixture of ahydrophobic urethane oligomer and an acrylic monomer and contains 1% byweight of a reaction initiator. Five percent by weight of this mixtureand 95% by weight of the liquid crystal material were mixed to prepare aliquid crystal mixture. At this time, the materials were heated at 90°C. and stirred so that the resinous material might be mixed well intothe liquid crystal material, until the liquid crystal material showedanisotropy.

The above-described liquid crystal mixture was injected into the liquidcrystal cell by a well-known method. During this injection, thetemperature was set to 90° C. Under a vacuum, the mixture was slowlycooled at a rate of 2° C./hr. As a result, molecules of the liquidcrystal mixture 116 held between the substrates were oriented along oneaxis in the same way as molecules of ordinary liquid crystal materials.

After the orientation step described above, the mixture was irradiatedwith ultraviolet radiation to precipitate (deposit) the resinousmaterial and to form the resinous columns 117 substantially orthogonalto the substrates. The UV irradiant intensity was 20 mW/cm². Theirradiation time was 1 minute. The resinous columns are used as spacers.

In the present example, the following four samples A-D were made andtheir characteristics were measured.

(1) A mixture of a hydrophobic urethane oligomer and an acrylic monomerin a weight ratio of 10:90. Since the reaction initiator was less than1% by weight, it was neglected.

(2) A mixture of an urethane oligomer and an acrylic monomer in a weightratio of 17:83.

(3) A mixture of an urethane oligomer and an acrylic monomer in a weightratio of 25:75.

(4) A mixture of an urethane oligomer and an acrylic monomer in a weightratio of 34:66.

Table 1 below shows acrylic monomer contents (weight %) of uncuredresins each consisting of a urethane oligomer and an acrylic monomer,the contact angles of the cured resins with respect to pure water, andthe contrast of each formed liquid crystal cell.

                  TABLE 1                                                         ______________________________________                                               oligomer content                                                                          contact angle of resin with                                resin  of resin    respect to pure water                                                                           contrast                                 ______________________________________                                        A      10%         49.4°      37.38                                    B      17%         51.0°      42.45                                    C      25%         55.8°      62.97                                    D      34%         66.0°      78.65                                    ______________________________________                                    

It can be seen from Table 1 that as the monomer content of the resindecreases, i.e., as the percentage of the hydrophobic urethane oligomerdecreases, the contact angle of the resin with respect to pure waterincreases, thus increasing the hydrophobic nature. This enhances thecontrast of the liquid crystal cell.

FIG. 2 shows the relation of the sensitivity of a photo-multiplier tothe contact angle of each liquid crystal cell fabricated in the presentexample under bright condition. In the measurement, a triangular wave of±30 V was applied across the cell. As can be seen from Table 1, thisrelation corresponds to the samples A-D. It can be seen from FIG. 1 thatdata about the samples have no great difference.

FIG. 3 shows the relation of the sensitivity of the photomultiplier tothe contact angle of each liquid crystal cell fabricated in the presentexample under dark condition. It can be seen from FIG. 3 that as thepercentage of the hydrophobic urethane oligomer is increased, thephotomultiplier sensitivity decreases, thus creating a darker state.That is, the dark state becomes more noticeable.

FIG. 4 shows the relation of the contrast ratio of each liquid crystalcell fabricated in the present example to the contact angle. In themeasurement, a triangular wave of ±30 V was applied across the cell. Itcan be seen from FIG. 4 that as the percentage of the hydrophobicurethane oligomer increases, the contrast ratio increases.

The results of these measurements reveal that the opticalcharacteristics of the liquid crystal display can be enhanced by addinga hydrophobic urethane oligomer to an uncured resin which is mixed witha liquid crystal material. Also, it can be seen that where the ratio ofthe hydrophobic urethane oligomer is more than 20% by weight, a contrastratio exceeding 40 can be obtained, and that a contrast ratio exceeding40 can be derived by setting the contact angle of the resin with respectto pure water larger than 50 degrees.

In the present example, a ferroelectric liquid crystal which has alayered structure and is affected greatly by bending of the substratesis used. In other words, the effects become more conspicuous. Otherliquid crystal materials may also be employed. Obviously, the novelconfiguration is not limited to simple matrix liquid crystal displays.For example, the novel configuration may also be applied to activematrix liquid crystal displays using TFTs and MIM devices.

EXAMPLE 2

Indium tin oxide (ITO) which is an electrode material was deposited on aglass substrate 10 cm square to a thickness of 500-2000 Å by sputteringor evaporation. In the present example, the thickness was 1000 Å. Thefilm was patterned by an ordinary photolithography process to form anelectrode pattern. Polyimide was applied to the laminate by spin coatingand then baked at 280° C. RN-305 produced by Nissan Kagaku Kogyo, Japan,and LP-64 produced by Toray, Japan, were used as the polyimide which wasused as the material of an orientation film. The thickness of thepolyimide film was 100-800 Å. In the present example, the thickness was150 Å. This substrate was rubbed to orient the molecules along one axis.Another substrate was fabricated similarly. Spherical silica particleswere dispersed as spacers on one of these two substrates. A sealingmaterial of epoxy resin was screen printed on the other substrate. Bothsubstrates were bonded together with a spacing of about 1.5 μm. Thus, acell was formed.

The liquid crystal material used in the present example wasferroelectric liquid crystal CS1014 produced by Chisso Corporation,Japan. Ps of this liquid crystal material was 5.4 nC/cm². The phasesequence was I (isotropic phase)-N (nematic phase)-A (smectic A phase)-C(smectic C* phase). The resinous material used in the present examplewas a mixture of a urethane oligomer and an acrylic monomer both ofwhich are commercially available.

Ninety five % by weight of the above-described liquid crystal materialand 5% by weight of an uncured resinous material were mixed up, heatedat 90° C., and stirred until the liquid crystal material showedisotropic phase or nematic phase. In this way, the resinous material wasuniformly dispersed in the liquid crystal material. A liquid crystalcell and the liquid crystal mixture were heated to 90° C. The liquidcrystal mixture was injected into the cell under a vacuum. After theinjection, the cell was slowly cooled down to room temperature at a rateof 2°-20° C./hr, in the present example 2° C./hr. Orientation at roomtemperature was observed with a polarization microscope. As a result, wehave found that the resinous material was sporadically distributed inthe cell. The molecules of the liquid crystal material were orientedalong one axis, i.e., along the rubbing direction of the orientationfilm, in the same way as a liquid crystal material to which no resin hasbeen added. In this manner, a good quenching position was obtained.

This cell was-irradiated with ultraviolet radiation having a strength of3 to 30 mW/cm² for a time of 0.5 to 5 min to cure the resin. In thepresent example, the strength was 20 mW/cm², and the irradiation timewas 1 min. After the UV irradiation, the molecules of the liquid crystalmaterial were kept oriented along one axis, i.e., along the rubbingdirection, and a good quenching position was obtained.

A triangular wave of ±30 V was applied across the cell, and its opticalcharacteristics were measured. Careful observation of the operation hasrevealed that light was quenched around the resin in a dark displaycondition although the amount of the quenching was quite small. At thistime, an arbitrary value indicating the bright state was 35.26. Anarbitrary value indicating the dark state was 1.131. The contrast ratiowas 31.16. A pulse of ±20 V was applied for 60 μm. Under this condition,the voltage holding ratio was 45.0%. The cell was caused to age. The ageis carried out by heating the liquid crystal material until the liquidcrystal material shows isotropic phase or nematic phase followed bycooling the liquid crystal material. Then, the cell was observed withthe naked eye. The quenching of light around the resin was improvedconsiderably. At this time, an arbitrary value indicating the brightstate was 40.08. An arbitrary value indicating the dark state was 0.924.The contrast ratio was 43.39. The voltage holding ratio was 49.0%. Theactual characteristics were improved greatly.

EXAMPLE 3

The present example is similar in structure to Example 2 and uses thesame liquid crystal material and the same resinous material as thoseused in Example 2.

Eighty five % by weight of the above-described liquid crystal materialand 15% by weight of the uncured resinous material were mixed up, heatedat 90° C., and stirred until the liquid crystal material showedisotropic phase, thus forming a liquid crystal mixture. A liquid crystalcell and the liquid crystal mixture were heated to 90° C. The liquidcrystal mixture was injected into the cell under a vacuum. After theinjection, the cell was slowly cooled down to room temperature at a rateof 2°-20° C./hr, in the present example 2° C./hr. Orientation at roomtemperature was observed with a polarization microscope. As a result, wehave found that the resinous material was sporadically distributed inthe cell. The molecules of the liquid crystal material were orientedalong one axis, i.e., along the rubbing direction of the orientationfilm, in the same way as a liquid crystal material to which no resin hasbeen added. In this manner, a good quenching position was obtained.

This cell was irradiated with ultraviolet radiation having a strength of3 to 30 mW/cm² for a time of 0.5 to 5 min to cure the resin. In thepresent example, the strength was 20 mW/cm², and the irradiation timewas 1 min. After the UV irradiation, the molecules of the liquid crystalmaterial were kept oriented along one axis, i.e., along the rubbingdirection, and a good quenching position was obtained.

A triangular wave of ±30 V was applied across the cell, and its opticalcharacteristics were measured. Careful observation of the operation hasrevealed that light was quenched around the resin in a dark displaycondition although the amount of the quenching was quite small. At thistime, an arbitrary value indicating the bright state was 22.89. Anarbitrary value indicating the dark state was 3.491. The contrast ratiowas 6.6. The voltage holding ratio was 61.0%. The cell was made to ageand then observed with the naked eye. The quenching of light around theresin was improved considerably. At this time, an arbitrary valueindicating the bright state was 31.48. An arbitrary value indicating thedark state was 3.162. The contrast ratio was 10. The voltage holdingratio was 71.0%. The actual characteristics were improved greatly.

EXAMPLE 4

Indium tin oxide (ITO) which is an electrode material was deposited on aglass substrate 10 cm square to a thickness of 500-2000 Å by sputteringor evaporation. In the present example, the thickness was 1000 Å. Thefilm was patterned by an ordinary photolithography process to form anelectrode pattern. Orientation film materials were applied to thelaminate by spin coating and then baked. Three kinds of orientation filmmaterial were used. This substrate was rubbed to orient the moleculesalong one axis. Another substrate was fabricated similarly. Sphericalsilica particles manufactured by Shokubai Kasei, Japan, were dispersedas spacers on one of these two substrates. A sealing material of epoxyresin was screen printed on the other substrate. Both substrates werebonded together with a spacing of about 1.5 μm. Thus, a cell was formed.

One liquid crystal material used in the present example wasferroelectric liquid crystal A having a phase sequence I (isotropicphase)-N (nematic phase)-A (smectic A phase)-C (smectic C* phase).Another liquid crystal material used in the present example wasferroelectric liquid crystal B having a phase sequence I-A-C. Acommercially available UV curable resin having a surface tension of 50.1dyne/cm was used.

Ninety five % by weight of the above-described liquid crystal materialand 5% by weight of the uncured resinous material were mixed. In orderto mix up these two materials, they were heated and stirred until theliquid crystal material showed isotropic phase or nematic phase. In thisway, the resinous material was uniformly dispersed in the liquid crystalmaterial, thus forming a liquid crystal mixture.

A liquid crystal cell and the liquid crystal mixture were heated untilan isotropic phase or a nematic phase was obtained. The liquid crystalmixture was injected into the cell under a vacuum. After the injection,the cell was slowly cooled down to room temperature at a rate of 2°-20°C./hr, in the present example 2° C./hr. Orientation at room temperaturewas observed with a polarization microscope. As a result, we have foundthat the molecules of the liquid crystal materials A and B were orientedhorizontally and that the resinous material was sporadically dispersedin the cell.

This cell was irradiated with ultraviolet radiation having a strength of3 to 30 mW/cm² for a time of 0.5 to 5 min to cure the resin. In thepresent example, the strength was 20 mW/cm², and the irradiation timewas 1 min. The resinous material was cured into columns and sporadicallydispersed in the cell. The orientation of this liquid crystal in thecell was measured. A triangular wave of ±30 V was applied across thecell, and its optical characteristics were measured. The results areshown in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        orientation                                                                             surface tension                                                                            contrast ratio                                                                          contrast ratio                               film material                                                                           (dyne/cm)    A         B                                            ______________________________________                                        1         69.67        77.5      78.9                                         2         61.31        56.4      16.9                                         3         51.00         4.17     15.2                                         ______________________________________                                    

The results show that the values indicating bright state did not differgreatly and that the values indicating dark state are increased as thesurface tension of the orientation film became greater than the surfacetension of the resinous columns. As a result, the contrast ratio wasalso enhanced.

The surface tension of the orientation film of a vertically orientedliquid crystal display was reduced for a give surface tension of theresinous material. The values indicating dark state were increased. As aresult, the contrast ratio was enhanced.

As described thus far, the present invention can improve the orientationof the liquid crystal molecules of a liquid crystal display usingpolymerized column spacers. Also, the contrast ratio can be improved.Furthermore, a liquid crystal display providing a high contrast ratiocan be obtained. In this display, resinous columns precipitated(deposited) out of an uncured resin maintain the substrates in intimatecontact with each other. A hydrophobic resinous material is added to theuncured resin which is mixed with a liquid crystal material.

A liquid crystal display uses resinous columns which are formed byadding a resinous material to a liquid crystal material andprecipitating (depositing) the resinous material out of the liquidcrystal material. In fabrication of this liquid crystal display, if anaging step according to the invention is added, then the orientation ofthe liquid crystal material is prevented from being disturbed althoughthe formed resinous columns shrink after they are cured. Hence, thevoltage holding ratio and the optical characteristics can be improved.

The present invention can be applied to various kinds of liquid crystalssuch as nematic liquid crystals and ferroelectric liquid crystals. Also,the invention can be used in active matrix devices and other variousdevices using a simple matrix structure or switching devices.

What is claimed is:
 1. An electro-optical device comprising:a pair ofsubstrates; an electro-optical modulating layer provided between thesubstrates and comprising a liquid crystal material and a resinousmaterial, said resinous material comprising a hydrophilic material, saidliquid crystal material comprising a molecule oriented substantiallyorthogonal to the substrates; and a columnar spacer provided between thesubstrates and comprising said resinous material.
 2. The device of claim1 wherein the resinous material is adhesive.
 3. The device of claim 1wherein the columnar spacer is substantially orthogonal to thesubstrates.
 4. The device of claim 1 wherein the molecule is oriented bya homeotropic alignment film provided on at least one of the substratesand in contact with the liquid crystal material.
 5. The device of claim1 wherein said liquid crystal is a ferroelectric liquid crystal.
 6. Anelectro-optical device comprising:a pair of substrates; anelectro-optical modulating layer provided between the substrates andcomprising a liquid crystal material and a resinous material, saidresinous material having a structure exhibiting a hydrophilic property,said liquid crystal material comprising a molecule orientedsubstantially orthogonal to the substrates; and a columnar spacerprovided between the substrates and comprising said resinous material.7. The device of claim 6 wherein the resinous material is adhesive. 8.The device of claim 6 wherein the columnar spacer is substantiallyorthogonal to substrates.
 9. The device of claim 6 wherein said liquidcrystal is a ferroelectric liquid crystal.
 10. An electro-optical devicecomprising:a pair of substrates; an electro-optical modulating layerprovided between the substrates and comprising a liquid crystal materialand a resinous material; an orientation film provided on an innersurface of at least one of the substrates to orient molecules of theliquid crystal material in a direction substantially orthogonal to thesubstrates; and a columnar spacer provided between the substrates andcomprising the resinous material, wherein the orientation film has asurface tension smaller than that of the columnar spacer.
 11. The deviceof claim 10 wherein said liquid crystal is a ferroelectric liquidcrystal.
 12. An electro-optical device comprising:a pair of substrates;an electro-optical modulating layer provided between the substrates andcomprising a liquid crystal material and a resinous material; anorientation film provided on an inner surface of at least one of thesubstrates to orient molecules of the liquid crystal material in adirection substantially orthogonal to the substrates; and a columnarspacer provided between the substrates and comprising the resinousmaterial, wherein the orientation film has a force which attracts liquidcrystal molecules of said liquid crystal material.
 13. The device ofclaim 12 wherein said liquid crystal is a ferroelectric liquid crystal.14. An electro-optical device comprising:a pair of substrates; anelectro-optical modulating layer provided between the substrates andcomprising a liquid crystal material and a resinous material; anorientation film provided on an inner surface of at least one of thesubstrates to orient molecules of the liquid crystal material in adirection substantially parallel to the substrates; and a columnarspacer provided between the substrates and comprising the resinousmaterial, wherein the orientation film has a force which attracts liquidcrystal molecules of said liquid crystal material.
 15. The device ofclaim 14 wherein said liquid crystal is a ferroelectric liquid crystal.16. An electro-optical device comprising:a pair of substrates; anelectro-optical modulating layer provided between the substrates andcomprising a liquid crystal material and a resinous material; anorientation film provided on an inner surface of at least one of thesubstrates to orient molecules of the liquid crystal material in adirection substantially orthogonal to the substrates; and a columnarspacer provided between the substrates and comprising the resinousmaterial, wherein the orientation film has a force which attracts liquidcrystal molecules of said liquid crystal material; wherein said liquidcrystal material is separated from said resinous material; and wherein asurface tension of said resinous material is greater than that of saidorientation film.
 17. The device of claim 16 wherein said liquid crystalis a ferroelectric liquid crystal.